1. Field of the Invention
The present invention relates to a method of preventing polymer scale deposition on the inner wall surface and so forth of a polymerization vessel during polymerization of a monomer having an ethylenically double bond.
2. Description of the Prior Art
In processes of preparing polymers by polymerizing a monomer in a polymerization vessel, the problem that polymer deposits on the inner wall surface and so forth in the form of scale, is known.
The deposition of the polymer scale on the inner wall results in disadvantages that the yield of the polymer and the cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into manufactured polymer, thereby impairing the quality of the manufactured polymer; and that removal of such polymer scale is laborious and hence time-consuming. Further, since the polymer scale contains unreacted monomer and operators may be exposed thereto, which may cause physical disorders in the operators.
Heretofore, as methods for preventing polymer scale deposition on the inner wall surface and so forth of a polymerization vessel, methods in which a suitable substance is coated on the inner wall surface, etc. as a scale preventive agent.
As the suitable substance acting as a scale preventive agent, there has been disclosed, for example, particular polar compounds (Japanese Patent Publication (KOKOKU) No.30343/1970), a dye or pigment (Japanese Patent Publication (KOKOKU) Nos. 30835/1970, and 24953/1977), etc.
In the meantime, vinyl chloride polymers obtained by polymerization are required to have a good whiteness; specifically, they are required to have an L value according to the Hunter's color difference equation, which is described below, of 70 or more.
The prior art polymer scale preventive agents include a great number of colored substances as exemplified typically by the dyes and pigments described in Japanese Patent Publication (KOKOKU) No. 30835/1970 or 24953/1977, the aromatic amine compounds described in Japanese Pre-examination Patent Publication (KOKAI) No. 50887/1976, and the reaction products of a phenolic compound and an aromatic aldehyde described in Japanese Pre-examination Patent Publication (KOKAI) No. 54317/1980, etc. Due to this, presumably, where suspension polymerization, etc. of vinyl chloride or the like is carried out in a polymerization vessel in which a coating composed of the scale preventive agent above had been formed, colored polymers may be produced. That is, according to measurement of the lightness L in the Hunter's equation described in JIS Z 8730 (1980), the L may be measured to be 65 or less, and coloration is thereby confirmed. Presumably, the coloration is caused by incorporation of components of the coating which has dissolved or peeled into the polymerization system.
Further, many of the prior art polymer scale preventive agents are poisonous as represented by aniline, nitrobenzene, formaldehyde, etc. listed as examples of the polar organic compounds described in Japanese Patent Publication (KOKOKU) No. 30343/1970, and the pigments containing a heavy metal such as chromium and lead described in Japanese Patent Publication (KOKOKU) No. 30835/1970. The dyes described in Japanese Patent Publication (KOKOKU) Nos. 30835/1970 and 24953/1977 include some dyes that involve concern about carcinogenesis. Therefore, use of these substances may cause problems in safety of operators.